1. Field of the Invention
The present invention relates to a focus-adjusting unit.
This application is based on Japanese Patent Application No. 2008-048763, the content of which is incorporated herein by reference.
2. Description of Related Art
In known microscopes in the related art, optical elements having positive refractive power and negative refractive power are disposed between a light source and an objective lens, and the working distance of the objective lens is changed by varying a physical distance (for example, see Japanese Unexamined Patent Application, Publication No. 2005-70477).
In addition, microscopes in which an adapter lens can be attached to and detached from a finite objective lens have also been disclosed (for example, see Japanese Unexamined Patent Application, Publication No. 2006-79000). With this configuration, by combining a small-diameter finite objective and an adapter lens and by moving the adapter lens in the optical axis direction, the working distance of the objective lens can be changed.
There are also known microscopes in which a finite objective lens can be attached and detached (for example, see Japanese Unexamined Patent Application, Publication No. 2006-139181). With this type, by combining a finite objective with an image-forming lens and by moving the image-forming lens along the optical axis direction, the working distance of the objective lens can be changed.
However, in the microscopes disclosed in these Applications, the positional relationship between the optical system for varying the focus and the objective lens and image-forming lens is not considered at all. Unless the positional relationship of the optical system is considered, if the working distance of the objective lens changes as the lenses constituting the optical system are moved in the optical axis direction, the problem of a significant change in the observation magnification is likely.